support never (YousefED#308)

Author: j-xzy

test/programs/never/main.ts

@@ -0,0 +1,4 @@
+export interface Never {
+  neverProp: never;
+  propA: string;
+}

test/programs/never/schema.json

@@ -0,0 +1,12 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "properties": {
+      "propA": {
+          "type": "string"
+      }
+  },
+  "required": [
+      "propA"
+  ],
+  "type": "object"
+}

test/schema.test.ts

@@ -230,6 +230,7 @@ describe("schema", () => {
         // see https://github.com/epoberezkin/ajv/issues/725
         // assertSchema("type-function", "MyObject");
         assertSchema("any-unknown", "MyObject");
+        assertSchema("never", "Never");
     });
 
     describe("class and interface", () => {

typescript-json-schema.ts

@@ -711,6 +711,11 @@ export class JsonSchemaGenerator {
 
         const clazz = <ts.ClassDeclaration>node;
         const props = this.tc.getPropertiesOfType(clazzType).filter(prop => {
+            // filter never
+            const propertyType = this.tc.getTypeOfSymbolAtLocation(prop, node);
+            if (ts.TypeFlags.Never === propertyType.getFlags()) {
+                return false;
+            }
             if (!this.args.excludePrivate) {
                 return true;
             }